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Route Survey Buoy (ambient noise)

This new technique provides a cost effective means of performing rapid-large area survey of the ocean bottom. Such broad-brush surveys could be followed up by conventional off-shore seismic profiling to provide high resolution views of regions of interest. Thus this technique is complementary to conventional seismic surveying with the potential for augmenting our current capabilities.

The ANSSB is a freeley drifting, navigated, large-area surveying buoy which could be used repeatedly (a number of times) in the quasi autonomous or autonomous mode of operation. The standard version of the buoy measures by means of ambient noise the geo acoustical properties of the sea bed. The buoy could be extended to a multi-sensor system.

The spatial structure of ambient noise in shallow water is governed by the geo-acoustic properties of the sea bed. By inverting data on the vertical coherence of broad band ambient noise estimates of the compressional and shear speeds of the bottom can be obtained. Thus the acoustic properties of the sea bed are determined without the use of a dedicated sound source.

Data from the Standart Buoy

• air temperature
• bathymetry along the track
• sound speed profile along the track
• ambient noise spectrum in water column (0.2Hz to 5KHz)
• GPS buoy position data
• GPS buoy drift-velocity data
• Geo-acoustic parameters of the sea bed

Compressional wave speed

• compressional wave absorption
• porosity
• density
• grain size
• layers of sediment
• High reliability and maintainability
• shear speed

Optional Environment Sensors

• Echo sounder to give the bathymetry along the track
• Thermistor to give air temperature above the surface
• Open system architecture
• Thermistor chain below surface to give sound speed profile along the track

Optional Hydrophone

• Vertical array of hydrophones and
• Thermistor to give air temperature above the surface on-board beamformer to improve signal detection against quiet targets (submarine)

Operating procedure

• Several of the freely drifting buoys could be deployed at different positions in the sea-area of interest.

In the quasi-autonomous mode of operation, the position of each buoy will be relayed back to the ship at regular intervals, where the position will be plotted automatically on an electronic sea chart (ECDIS). An automatic alarm will be activated if a buoy moves off track (for instance, if picked up by a fishing vessel). The environmental data will be stored and processed on board of the buoy.

In the autonomous mode of operation all the environmental data will be stored and processed on board the buoy. At the end of the mission, an on-board transponder will be used to find the buoy, which will be recovered and the processed data downloaded. After replacing the batteries and resetting the data collecting system the buoy will be ready for the next deployment.